Setup:

Whenever I have intense activity on the 2nd channel (burn/copy), it seems all the juice is taken and my HD slows down big time (even with the one I had before with this setup). Example: I’m listening to an mp3 from the HD, start to burn a CD, and BANG! the mp3 plays half the speed!

IDE can only access one drive at a time. So why its using your 2nd drive it cant use the 1st drive untill the 2nd drive is stopped being used. I advise you not to put a cdrom on the same channel as a Hard drive if you are going to be using them at the same time. Maybe you can get a program that pre loads the mp3 into RAM.